Republican presidential nominee Donald Trump promised us an unprecedented convention. Boy, has he delivered.

For three nights, speakers successfully prosecuted Hillary Clinton. For three nights, they failed to make the case that Trump is a credible commander in chief. The gap between these two threshold convention goals was stark early Wednesday; it blew apart with the force of a supernova when Ted Cruz, a vanquished opponent who refused to release his delegates and has his eyes set on the 2020 race, pointedly, unsubtly, and ungracefully declined to endorse him.

Even as Cruz made a powerful case against Clinton, he could not bring himself to say that Trump was the better choice. By implication, Cruz was leaning in to a Trump loss in November. The implication was not lost on the audience, who began to boo and jeer. It was not lost on Trump, who suddenly appeared in the convention hall, trying to placate the crowd with an upturned thumb.

Cruz's prepared remarks went for nine minutes. He spoke for 23. The wisdom of letting him speak at all was lost on me; has Cruz ever given anyone the impression that he's in it for anyone but himself? He outfoxed Donald Trump, clearly, and probably outfoxed himself; the reaction, even by his supporters, to his endorsement ghosting will probably hurt his chances in four years.

As the convention audience tried to digest all of this — surely, more drama than any convention in modern memory has given us — the clock hit 10 p.m., and tens of millions of more people tuned in. They heard Trump's son Eric speak movingly about his father. The nominee teared up at the end.

Then Newt Gingrich came on. He decided to lecture the audience. They misunderstood Cruz, he insisted. When Cruz said, "You can vote your conscience to anyone who will uphold the Constitution," Cruz meant, of course, that "in this election, there is only one candidate who will uphold the Constitution." Gingrich continued: "To paraphrase Ted Cruz, the only possible candidate this fall is the Trump-Pence Republican ticket."

But of course, Cruz did not say that. Gingrich's damage-control mind-reading could not bring back the oxygen that Cruz's selfish stand for principle had sucked out of the room.

No doubt true: A candidate with character flaws as large as Trump's needs to fully discredit Clinton in order to win in November. Negative energy is a better bet.

But Trump has not crossed the basic threshold of plausibility. He is not giving recalcitrant Republicans, or independents, really, a reason to go to the polls. He is giving Democrats plenty of reasons to turn out for Hillary Clinton.

Replicating the seat-of-his-pants scorched earth strategy that worked in the primaries gets him a plurality of a minority of the popular vote and delivers to Clinton a resounding victory in the electoral college. That's why a well-orchestrated convention, free of unforced errors, dynamic and interesting, is essential.

The Republican vice presidential nominee, Gov. Mike Pence, gave an acceptance speech as graceful as Cruz's was gauche. But it will be Cruz whose vignettes will go viral, not Pence's. The same media environment that Trump mastered to win the nomination will ensure that his foul-ups will loop endlessly while his good choices get mediocre notice.

On Tuesday, as the 10 p.m. super-primetime hour approached, I had the same feeling: It looked like Trump could pull himself out of the hole created by his wife Melania's plagiarism flap.

His two children delivered deftly constructed speeches. Tiffany Trump, 22, spoke of a doting father who cared less about her grades and more that his little girl was happy in school. Donald Trump Jr., a true conservative, spoke of the hard work and humility his "hero" Dad imparted to him. The latter managed to take up a good chunk of the 10 o'clock hour, when tens of millions of people tune in because the major networks begin their coverage. It was a good start.

But then Lucifer messed with the program. Inexplicably, a charged-up Dr. Ben Carson, a vanquished Trump rival with a narrow range of vision, was given prime time real estate to pull out phrases that meant something only to a slab of the Republican base. The man who Trump once mocked as having "lower energy than Jeb" spent two minutes on political correctness. "I hate political correctness. It is antithetical to the founding principles of this country." When the audience predictably cheered, he stepped on his own lines: "Don't eat up my time!" he implored.

He abandoned his prepared remarks. He implied that Hillary Clinton was in a league with the devil. Her hero, he said, was Saul Alinsky, dropping the name of an obscure socialist labor organizer as if he were Bono. And Alinsky "acknowledges Lucifer," Carson insisted.

Carson did not manage to make much of a case for Trump. He just wanted everyone to know how bad a Clinton administration would be.

That's not a bad message for a convention that is designed to cast Clinton as a crook more than it is to sell Trump as a president. But the messenger couldn't deliver. For some reason, organizers decided to fill the rest of the 10 o'clock hour with two ordinary people — a soap opera star and the founder of American Muslims for Trump. He delivered the final benediction. On television, delegates, wanting to get to those buses before big lines formed, were seen walking out. Not a good image.

Why didn't the younger Trump daughter, whose speech charmed everyone, get that time? For that matter, why didn't Chris Christie, who prosecuted a blistering case against Clinton when he spoke earlier, get a better speaking slot?

Christie had the audience cheering, over and over, "Lock her up, Lock her up." His speech was mean, and over the top, and it violated the norms of politics, but his party knows that the only way their nominee can win is if millions of Americans who plan to vote for her decide instead that her conduct in office disqualifies her from being president. For what Republicans needed to do, it was effective. And many, many fewer people saw it than who might have.

Trump has one more shot to put it all together.